operations all the smaller avenues of the building were erected, of the different heights of one, two, or three storeys. The greatest number of columns thus fixed in one week was 310. [Illustration: FIXING THE GIRDERS.] [Illustration: General View of the Works in Progress.] Hoisting the Roof Trusses. The wrought-iron roof-trusses over the 48-feet avenues were raised in a similar manner to the columns and girders; and in all cases horses were employed to run out the end of the fall-rope, which was passed through a pulley or catch-block at the foot of the shear-legs, in order to change its direction from vertical to horizontal. For raising the roof-trusses of seventy-two feet span over the main avenue a somewhat different method was employed. A single mast or derrick, more than seventy feet high, was placed in the centre of the avenue, and steadied in an upright position by guide-ropes spreading from the top in various directions. Near its summit the hoisting-tackle was firmly lashed on. The trusses to be hoisted were brought from the places where they had been put together, and placed across the main avenue at the points where they were to be fixed. Two ends of a stout chain were passed round the upper portion of the truss, at points dividing its length into about three equal parts. To this chain the hoisting-tackle was attached, guide-ropes being further fastened to each end of the truss to steady it in its ascent. In order to stiffen the truss horizontally, struts were attached at the centre projecting on each side, and held in their place by tie-rods attached to the upper part of the truss, and forming a triangle on each side. Before the truss, therefore, could bend in a horizontal direction, the attachment of these tie-rods must have given way. Six horses drew out the end of the fall-rope, and in the course of a very few minutes the truss was hoisted to its giddy height, and each end slipped in between the projections made in the connecting-pieces to receive it.